Hydrous silica for rubber-reinforcing filler

ABSTRACT

The present invention pertains to a hydrous silica for rubber-reinforcing filler, having a BET specific surface area ranging from 230 to 350 m 2 /g, and satisfies the following: a) the pore volume of 1.9 nm to 100 nm pore radius measured by the mercury press-in method (V HP-Hg ) ranges from 1.40 to 2.00 cm 3 /g; b) total pore volume in the range of 1.6 nm to 100 nm pore radius by the nitrogen adsorption/desorption method (V N2 ) ranges from 1.60 to 2.20 cm 3 /g; and c) the pore volume ratio of (a) and (b) V HP-Hg /V N2  ranges from 0.70 to 0.95. This invention provides a hydrous silica capable of further improving reinforcing properties of a rubber, particularly the wear resistance by improving dispersibility of the hydrous silica in the rubber in addition to rubber reinforcing properties obtained by a high BET specific surface area.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2018-151033, filed Aug. 10, 2018, the entire disclosure of which isspecifically incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hydrous silica for rubber reinforcingfiller. In particular, the present invention provides a hydrous silicafor rubber reinforcing fillers which can achieve a high degree ofdispersibility and provide a high reinforcing property, (particularlythe wear resistance), when compounded in tires and various industrialrubber products.

BACKGROUND OF THE INVENTION

Carbon black has long been used as a reinforcing filler for rubber. Onthe other hand, in recent years, hydrous silica has been widely used asa white reinforcing filler for the reason that it is possible to reducerolling resistance and easily colorize rubber. In particular, in thecase where rubber being compounded hydrous silica is used for a tiretread, rolling resistance can be reduced, and therefore, in recentyears, a tread of a pneumatic tire containing hydrous silica hasattracted attention. In addition, hydrous silica is required to improvethe reinforcing properties of rubber (particularly the wear resistance),due to consideration for the environment, and the demand for hydroussilica is becoming increasingly high.

The hydrous silica has a silanol group (—SiOH) on its surface, andcombines with rubber molecules to contribute to the improvement of thereinforcing property. The number of silanol groups of hydrous silicaincreases as the specific surface area increases (the smaller theprimary particles described later). Therefore, it is said that thehydrous silica having a high specific surface area improves thereinforcing property of the rubber.

The main factors for improving the rubber reinforcing property of thehydrous silica are two of (1) high BET specific surface area and (2)good dispersibility. Hydrous silica has a structure in which primaryparticles of about 10 to 60 nm are aggregated to a particle size ofabout 2 to 100 μm, and the BET specific surface area is about 50 to 250m²/g. It is also known that as the BET specific surface area increases,the primary particles become smaller, and silanol groups on the surfaceare densely aggregated by hydrogen bonding, thereby increasing theaggregation strength. On the other hand, in the case of hydrous silicafor rubber reinforcing filler, it is important to increase the specificsurface area, but at the same time, the rubber reinforcement isincreased as the dispersibility is improved. From this viewpoint, it ispreferable that the aggregation is weak.

As a technique focusing on the BET specific surface area, there has beenknown an attempt to improve the rubber-reinforcing property byincreasing the BET specific surface area and adding an additive (patentdocument 1, 2).

Patent document 1 discloses a process for the preparation of hydroussilica for rubbers. Polycarboxylic acid and aluminum are added toenhance the bonding strength between the polymer and the hydrous silicato improve the reinforcing property. However, in the manufacturingmethod described in patent document 1, since acidic reactions are used,the resulting hydrous silica has a strong aggregation and is difficultto disperse.

Patent document 2 discloses inventions relating to hydrous silica withaluminum added to their surfaces. Hydrous silica having a high specificsurface area (here, a CTAB specific surface area of 160 m²/g or more)and a specified nitrogen pore distribution tends to be penetrated byrubber molecules. It is proposed to enhance the bonding strength withrubber molecules by adding aluminum to the surface of such hydroussilica to improve the reinforcing property.

An improvement in the dispersibility of hydrous silica is disclosed inpatent document 3. Patent document 3 evaluates dispersibility on thebasis of the wk ratio, and hydrous silica having a low wk ratio and gooddispersibility has been proposed. In patent document 3, at the same timeas improving dispersibility, Al₂O₃ is added to the hydrous silica toenhance the bonding strength between the polymers and the hydroussilica, thereby improving the reinforcing property. The hydrous silica(precipitated silica) described in patent document 3 has a Al₂O₃ contentof 2 to 5.0 wt % and a wk ratio of less than 3.4, a CTAB surface area of80 to 139 m²/g and a BET-specific surface area of 80 to 180 m²/g.

Patent document 1: JP-A-2017-514773 (WO2015/121332)

Patent document 2: JP-A-2017-2210

Patent document 3: JP-A-2000-72434

The entire description of patent documents 1 to 3 is specificallyincorporated herein by reference.

SUMMARY OF THE INVENTION

In addition to further improving the reinforcing property, particularlythe wear resistance, a hydrous silica having good dispersibility inrubber and good workability at the time of mixing operation has beendemanded more than in the past. However, in the hydrous silica describedin patent document 1 or 2, although the specific surface area isimproved, as described above, the hydrous silica having a high specificsurface area has a strong aggregation structure due to the small size ofthe primary particles, and therefore, satisfactory dispersibility cannotbe obtained. In the hydrous silica described in patent document 3, thedispersibility can be improved to some extent, but the specific surfacearea is not sufficient and the reinforcing property is not sufficient.

In addition, when hydrous silica having a high specific surface area isgranulated to improve handling performance, the aggregation structurebecomes stronger than that in the case of a low specific surface area,resulting in further deterioration of dispersibility. In particular, inthe process of patent document 1 in which synthesis is made byneutralization in acidic reaction, the BET specific surface area can beeasily increased, and at the same time, when the hydrous silica iscompounded (mixed) into the rubber, the hydrous silica is mixed quicklyat the stage of the initial mixing, so that the handling performance isvery excellent. However, on the other hand, even at the end of therubber compounding, the hydrous silica is not dispersed in the rubberand sufficient reinforcement cannot be obtained. It can be said thatthese dispersion defects do not contribute to the improvement of thereinforcing performance, and it is preferable that the dispersiondefects are small from the viewpoint of the quality stability.

There is a need to develop a hydrous silica for rubber reinforcingfiller having such a relatively high BET-specific surface area (e.g.,230 m²/g or more), which has improved dispersibility in rubber, furtherimproved wear resistance, and improved handling performance.

The problem to be solved by the present invention is to provide ahydrous silica for rubber reinforcing filler, which has improvedhandling performance when compounded into rubber, improveddispersibility in rubber, and desired tear strength and wear resistanceas rubber reinforcement in compounded rubber.

The rubber reinforcing property has been conventionally obtained in thecase of hydrous silica having a relatively high BET specific surfacearea (e.g., 230 m²/g or more) as described above, but the object of thepresent invention is to provide a hydrous silica capable of furtherimproving reinforcing properties of a rubber, particularly the wearresistance, by improving dispersibility of the hydrous silica in therubber in addition to rubber reinforcing properties obtained by a highBET specific surface area.

Means for Solving the Problem

The inventors of the present invention conducted various studies inorder to develop a hydrous silica having a high BET-specific surfacearea (e.g., 230 m²/g or more), which has improved handling performancewhen compounded into a rubber, and also improved dispersibility in therubber.

In particular, the inventors of the present invention have analyzed howthe hydrous silica is dispersed in the rubber as the mixing periodelapses when the hydrous silica is compounded into the rubber and mixed.Based on this analysis result, it was further examined what kind ofparticles structure and pore structure the hydrous silica has, can solvethe above problem.

The results show that a hydrous silica satisfying that

the BET specific surface area ranges from 230 to 350 m²/g;

a): the pore volume of 1.9 nm to 100 nm pore radius measured by themercury press-in method (V_(HP-Hg)) ranges from 1.40 to 2.00 cm³/g;

b): total pore volume in the range of 1.6 nm to 100 nm pore radius bythe nitrogen adsorption/desorption method (V_(N2)) ranges from 1.60 to2.20 cm³/g; and

c): the pore volume ratio of (a) and (b) V_(HP-Hg)/V_(N2) ranges from0.70 to 0.95,

is a hydrous silica with ideal performance as a hydrous silica forrubber-reinforced filler which simultaneously satisfies threeindependent performances of high BET specific surface area, highdispersibility and handling performance The present invention has beencompleted by this finding.

The present invention is as follows.

[1]

A hydrous silica for rubber reinforcing filler satisfying the followingBET specific surface areas and a) to c):

the BET specific surface area ranges from 230 to 350 m²/g;

a): the pore volume of 1.9-100 nm pore radius measured by the mercurypress-in method (V_(HP-Hg)) ranges from 1.40 to 2.00 cm³/g;

b): total pore volume in the range of 1.6 to 100 nm pore radius by thenitrogen adsorption/desorption method (V_(N2)) ranges from 1.60 to 2.20cm³/g; and

c): the pore volume ratio of (a) and (b) V_(HP-Hg)/V_(N2) ranges from0.70 to 0.95.

[2]

The hydrous silica according to [1], wherein the pore volume in therange of 100 nm to 1,000 nm of pore radius as measured by mercurypress-in method ranges from 0.50 to 1.00 cm³/g.

[3]

The hydrous silica according to any one of [1] to [2], wherein the porevolume in the range of 1.6 to 62 μm of pore radius measured by mercurypress-in method ranges from 0.18 to 0.80 cm³/g, and the hysteretic porevolume difference in the range of 10 to 400 kPa measured by mercurypress-in method is 0.07 cm³/g or more.

[4]

The hydrous silica according to any one of [1] to [3], wherein theresidual amount when classified with a sieve having an aperture of 200μm is 70% by weight or more of the total and the pellet hardness is inthe range of 5 to 35 cN.

[5]

The hydrous silica according to any one of [1] to [4], wherein CATBspecific surface area ranges from 200 to 350 m²/g.

[6]

The hydrous silica according to any one of [1] to [5], wherein pH of 4%by weight slurry is in the range of 5 to 8, the electric conductivity ofthe filtrate of the slurry is less than 1,000 μS/cm, and the moisturecontent is less than 9%.

[7]

The hydrous silica according to any one of [1] to [6], which is acompacted body.

Advantageous Effects of the Invention

According to the present invention, it is possible to provide a hydroussilica having excellent rubber reinforcing properties, particularly thewear resistance, in which the rubber reinforcing properties are added byimproving handling performance when compounded into the rubber, makingthe BET specific surface area within a predetermined range, andimproving dispersibility of the hydrous silica into the rubber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a comparison of the cumulative pore volume of the hydroussilica obtained in Example 1 with a pore radius of 100 nm or less asmeasured by the nitrogen adsorption/desorption method and the mercurypress-in method.

FIG. 2 is a pore distribution diagram including the cumulative porevolume of mercury press-in method 1 (measurement range r=1.9 to 6,400nm) obtained in Example 1.

FIG. 3 is a pore distribution diagram including the cumulative porevolume of the nitrogen adsorption/desorption method (measurement ranger=1.6 to 100 nm) obtained in Example 1.

FIG. 4 is a pore distribution diagram including the cumulative porevolume of mercury press-in method 2 (measurement range r=1.6 to 62 μm[1,600 to 62,000 nm]) obtained in Example 1.

MODES FOR CARRYING OUT THE INVENTION

<Hydrous Silica>

The present invention is a hydrous silica for rubber-reinforced fillerhaving the following characteristics:

the BET specific surface area ranges from 230 to 350 m²/g.

a): the pore volume of 1.9 to 100 nm pore radius measured by the mercurypress-in method (V_(HP-Hg)) ranges from 1.40 to 2.00 cm³/g,

b): total pore volume in the range of 1.6 to 100 nm pore radius by thenitrogen adsorption/desorption method (V_(N2)) ranges from 1.60 to 2.20cm³/g,

c): the pore volume ratio in a) and b) V_(HP-Hg)/V_(N2) ranges from 0.70to 0.95

In the hydrous silica of the present invention, when the BET specificsurface area is less than 230 m²/g, the reinforcing property isinadequate as in a conventional manner. As the BET specific surface areaincreases, the production of hydrous silica tends to be difficult, andthe production of hydrous silica having a BET specific surface area ofmore than 350 m²/g is practically difficult. The range of theBET-specific surface area is preferably 230 m²/g or more, morepreferably 240 m²/g or more, further more preferably 250 m²/g or more,preferably 340 m²/g or less, more preferably 330 m²/g or less, furthermore preferably 325 m²/g or less.

a): By the mercury press-in method, the pore volume in the range of 1.9nm to 6,400 nm can be measured by boosting the maximum pressure from 100kPa to 400 MPa. The hydrous silica of the present invention has a porevolume of 1.9 nm or more and 100 nm or less measured by mercury press-inmethod (V_(HP-Hg)) in the range of 1.40 to 2.00 cm³/g. The poredistribution measurement by the mercury press-in method is a method inwhich the pore distribution is obtained from the amount of pressurizingmercury, which is difficult to wet, into a sample and intruding into thesample. The pore distribution by the mercury press-in method of thepresent invention is the pore distribution obtained when the pressure isincreased (measured from the larger pore diameter), unless otherwisespecified.

V_(HP-Hg) below 1.40 cm³/g tends to lack rubber-reinforcement, and atmore than 2.00 cm³/g, it tends to be difficult to actually produce ahydrous silica. V_(HP-Hg) is preferably 1.50 cm³/g or more, morepreferably 1.60 cm³/g or more, preferably less than 1.95 cm³/g, morepreferably 1.90 cm³/g or less.

b): Total pore volume in the range of 1.6 nm to 100 nm pore radius bythe nitrogen adsorption/desorption method (V_(N2)) is in the range of1.60 to 2.20 cm³/g. The measurement of pore distribution by the nitrogenadsorption/desorption method is a method in which nitrogen gas moleculesare adsorbed on the surface of a sample in the range of vacuum toatmospheric pressure under liquid nitrogen (−196° C.) and desorbed inthe range of atmospheric pressure to vacuum, and the pore distributionis measured from the adsorption/desorption isotherm. The measurable poreradius range is 1.6 nm to 100 nm. The pore distribution by the nitrogenadsorption/desorption method of the present invention is the poredistribution obtained in the desorption distribution (measured from thelarger pore diameter).

V_(N2) less than 1.60 cm³/g lacks rubber reinforcement, and V_(N2)greater than 2.20 cm³/g tends to make actual production of hydroussilica difficult. V_(N2) is preferably 1.70 cm³/g or more, morepreferably 1.80 cm³/g or more, preferably 2.15 cm³/g or less, morepreferably 2.10 cm³/g or less.

Conventionally, hydrous silica of V_(HP-Hg)≥V_(N2) (V_(HP-Hg)/V_(N2)≥1)was known in common rubber-reinforced filling hydrous silica,particularly in rubber-reinforced filling hydrous silica having a BETspecific surface area of more than 230 m²/g. However, a hydrous silicawith V_(HP-Hg)≥V_(N2) (V_(HP-Hg)/V_(N2)≥1) is a tight aggregate whoseradius is less than 100 nm when it is mixed with rubber, so it remainsas a large aggregate even if it is dispersed in rubber. As a result, therubber molecules do not penetrate to the center of the aggregate,resulting in poor dispersion, and it is difficult to obtain sufficientrubber reinforcement.

When the pore distributions of the nitrogen adsorption/desorption methodand the mercury press-in method are compared with each other in therange of pore radius of 100 nm or less (the range of micropores tomacropores), when the BET specific surface area of the hydrous silica is230 m²/g or more, the aggregation strength of the hydrous silicagenerally increases as described above. Therefore, in particular, evenwhen the measurement is performed by the mercury press-in method inwhich the injection is made to the pressure of 400 MPa, the pores havingthe radius of 100 nm or less are not crushed by the pressure, the porevolume difference is equal to or the mercury pore volume being detectedlarger than the nitrogen pore volume (V_(HP-Hg) ≥V_(N2)) even incomparison with the nitrogen pore volume measured from the vacuum to theatmospheric pressure.

On the other hand, the hydrous silica of the present invention controlsthe aggregation structure, and therefore V_(HP-Hg) of pore distributionswith pore radius of 100 nm or less is in the range of 1.40 to 2.00cm³/g, and V_(N2) is in the range of 1.60 to 2.20 cm³/g. However, sincethe aggregation structure in the pore volume range of the presentinvention is weaker than the conventional hydrous silica having a BETspecific surface area of 230 m²/g or more, the aggregation structure isvery easily broken by the pressure measured by the mercury press-inmethod. Therefore, it is characterized that c): the pore volume ratio ofa) and b) V_(HP-Hg)/V_(N2) is in the range of 0.70 to 0.95. Hydroussilica with a V_(HP-Hg)/V_(N2) of less than 0.70 is difficult toproduce, and hydrous silica with a V_(HP-Hg)/V_(N2) of more than 0.95 isstrongly aggregated and difficult to disperse in rubber.

The pore volume ratio V_(HP-Hg)/V_(N2) preferably ranges from 0.75 to0.95, more preferably from 0.78 to 0.93.

In other words, with respect to the hydrous silica having the above porevolume ratio V_(HP-Hg)/V_(N2), the aggregate in the range of macroporesto mesopores, when expressed with the term of macropores to mesoporesused in catalyst society, is estimated to be more likely to collapsethan the conventional hydrous silica, and therefore, it is assumed thatthe hydrous silica is easily dispersed in the rubber and has excellentreinforcing properties.

The Embodiment Described in [2]

The hydrous silica of the present invention preferably has a pore volumeV_(MP-Hg) in the range of 100 nm to 1,000 nm (medium pressure range) asmeasured by the mercury press-in method in the range of 0.50 to 1.00cm³/g (the embodiment described in [2]).

If the pore volume V_(MP-Hg) is less than 0.50 cm³/g, there is atendency for either the aggregation structure in this area (macropores)to be too strong (consolidated at levels where the aggregation does notcollapse) or the aggregation structure to be extremely weak, so that thepores are crushed and solidified by the pressure of mercury. Therefore,even if mixed and dispersed in the rubber, there is a strong tendency toexist as hydrous silica aggregates in the rubber, and the improvement ofthe reinforcing property becomes insufficient in some cases.

Conversely, hydrous silica having a pore volume V_(MP-Hg) of more than1.00 cm³/g is often present in the form of fine particles of hydroussilica. Alternatively, the bulk specific gravity is low (light), anddust is generated even during mixing, which may cause deterioration ofthe working environment, and penetration into the rubber may becomedifficult. Therefore, the dispersion at the early stage of the time ofmixing is deteriorated, sufficient dispersion is not performed, andconsequently, the reinforcing property may be lowered.

The Embodiment Described in [3]

The hydrous silica of the present invention preferably has a pore volumeV_(LP-Hg) of 0.18 to 0.80 cm³/g in the range of pore radius of 1.6 to 62μm (low pressure range) as measured by the mercury press-in method.Further, the hydrous silica of the present invention preferably has apore volume (hysteretic pore volume difference in the range of 10 to 400kPa (low pressure range)) of 0.07 cm³/g or more when the pressure israised to 400 kPa and then lowered to 10 kPa by the mercury press-inmethod (the embodiment described in [3]).

If the pore volume V_(LP-Hg) is 0.18 cm³/g or more, the pressure densitybecomes too high and there is no cause of the dispersion failure, if thepore volume V_(LP-Hg) is 0.80 cm³/g or less, it is sufficient as ashape, and the handling performance is also good. The pore volumeV_(LP-Hg) more preferably ranges from 0.18 to 0.50 cm³/g.

If the difference in hysteretic pore volume is 0.07 cm³/g or more, itdoes not show a state in which it does not disperse at the early stageof mixing into rubber because the aggregation structure is too strong(good initial dispersibility). The hysteretic pore volume differentialis more preferably 0.10 cm³/g or greater.

The Embodiment Described in [4]

The hydrous silica of the present invention preferably has a residualcontent of not less than 70% by weight of the total weight whenclassified with a sieve having an aperture of 200 μm, and has a pellethardness of 5 to 35 cN (the embodiment described in [4]). If the amountof the residue when classified by a sieve having a sieve opening of 200μm is 70% by weight or more of the whole, the generation of dust can besuppressed while the handling performance is good. If the pellethardness is 5 cN or more, the generation of dust can be prevented, thehandling performance is good, and the dispersibility at the early stageis good. If the pellet hardness is 35 cN or less, the final dispersionperformance is also good.

The Embodiment Described in [5]

The hydrous silica of the present invention preferably has a CTABspecific surface area ranging from 200 to 350 m²/g (the embodimentdescribed in [5]). In the case of hydrous silica satisfying at least thecondition of the present invention described in [1], high reinforcementcan be obtained when compounded in rubber, and in addition, highreinforcement can be surely obtained when CTAB specific surface area iswithin the above ranges. When CTAB specific surface area is more than350 m²/g, it may be difficult to produce the hydrous silica per se. CTABspecific surface area is preferably 220 m²/g or more, more preferably240 m²/g or more.

In addition, in the hydrous silica of the present invention, BET/CTABratio, which is the ratio of the two specific surface areas,BET-specific surface area and CTAB specific surface area, preferablyranges from 1.0 to 1.2. When BET/CTAB ratio is 1.2 or less, a denseaggregate is not formed, and dispersibility in rubbers is good. Hydroussilica having a BET/CTAB ratio of 1.0 or more can be produced.

The Embodiment Described in [6]

The hydrous silica of the present invention preferably has an electricconductivity of filtrate of 4 wt % slurry less than 1,000 μS/cm, a pH of4 wt % suspension in the range of 5 to 8, a moisture content less than 9wt % (embodiment described in [6]). If the electrical conductivity isless than 1,000 μS/cm, aggregation is less likely to occur over time,more preferably less than 800 μS/cm, and further more preferably lessthan 500 μS/cm.

The pH ranging from 5 to 8 of the 4% by weight slurry is equivalent tothe pH of a conventional hydrous silica. If the pH is within this range,good vulcanization properties and reinforcing properties can beobtained.

Suitably, the hydrous silica of the present invention has a moisturecontent of less than 9%, and a moisture content of less than 9% isapproximately equivalent to the moisture content of conventional hydroussilica. If the moisture content is within this range, good vulcanizationproperties and reinforcing properties can be obtained. The electricalconductivity and pH can be controlled by a water washing step in themanufacturing process, and the moisture content can be controlled by adrying step.

<Preparation Process>

The hydrous silica of the present invention is a novel hydrous silicahaving an aggregation structure that differs from conventional hydroussilica, as described above. The process for the preparation of thishydrous silica will be explained by way of example (the process of thepresent invention will be referred to as a multistage process).

A synthetic method by the following multistage reactions can beexemplified, and the hydrous silica of the present invention can beobtained by a synthetic method including steps i) to vii). However, theconsolidation step vii) can be omitted if the granulation of the hydroussilica can be performed to some extent in step vi).

i) Pre-charging the reactor with an alkaline silicate solution adjustedto a specified pH (pH9.5 to 12),

ii) A neutralization reaction step including a step of dropping analkali silicate aqueous solution and a mineral acid simultaneously, anda step of dropping only mineral acid without adding an alkali silicateaqueous solution,

iii) A step of dropping the alkali silicate solution and the mineralacid simultaneously, provided that the respective flow rates areindependently in the range of 20 to 80% of the flow rate in the step ofdropping the alkali silicate solution and mineral acid simultaneously instep ii),

iv) A step in which only mineral acid is added dropwise without addingan aqueous solution of alkali silicate and the neutralization reactionis stopped at a pH<7.

However, steps i) to iv) are carried out while the reactant slurry isstirred and/or circulated while maintaining at the range of 70 to 90°C., and steps ii) to iii) are carried out while maintaining at the rangeof pH 9.5 to 12.

v) Filtration of the obtained hydrous silica slurry and washing withwater in an amount equal to or more than the cake of the obtainedhydrous silica,

vi) Drying step to adjust the moisture content of hydrous silica,

vii) A step of performing consolidation molding of the obtained hydroussilica.

The alkali silicate aqueous solution is not particularly limited, and,for example, commercially available sodium silicate can be used. Themineral acid is not particularly limited, but sulfuric acid ispreferable, and any of dilute sulfuric acid to concentrated sulfuricacid can be used as the concentration.

Steps i) to ii) are a preparation step for making the BET specificsurface area 230 m²/g or more and a preparation step for forming a porevolume with a radius of 100 nm or less. In step i), for example, acommercially available aqueous alkali silicate solution is diluted withwater and adjusted to a predetermined pH. As long as pH can bemaintained within a predetermined pH range, it may or may not besupplemented with other compound such as salts.

The order of the step of dropping the alkali silicate aqueous solutionand the mineral acid simultaneously and the dropping only the mineralacid without adding the alkali silicate aqueous solution in step ii) arein random. For example, the step of dropping only the mineral acidwithout adding the alkali silicate aqueous solution may be performed inany of the first half, the intermediate half, and the second half of thestep ii).

Step iii) is a newly added step in the present invention which is notpresent in the conventional process. By adding this step, it is possibleto control the pore volume and structure of pores having a radius of 100nm or more and 1,000 nm or less while forming structure of pores havinga radius of 100 nm or less. Step iii) may be performed, for example, ata constant flow rate in the range of 20% to 80% for the simultaneousdropping step of step ii), or may be performed by changing the flow rateat least once in the above range in the middle of the step. The flowrates of the aqueous alkali silicate solution and the mineral acidpreferably range from 20 to 60% of the flow rates of the aqueous alkalisilicate solution and the mineral acid in step ii) from the standpointof obtaining a hydrous silicate having the desired structure.

It is recommended that steps ii) and iii) be completed in a total ofabout 80 to 140 minutes, preferably about 100 to 130 minutes. The stepsii) and iii) may be repeated two or more times. That is, for example,the first step ii) and step iii) may be carried out, and then the stepiv) may not be carried out, but the steps ii) and iii) may be carriedout again, and then the step iv) may be carried out. The repetition ofsteps ii) and iii) can be carried out, for example, twice, three timesor four times. Repeating steps ii) and iii) advantageously facilitatesobtaining hydrous silica having the desired structure properties.

The hydrous silica of the present invention is maintained in theneutralizing reaction step at least pH7, preferably pH10.0 to 12.0, morepreferably pH11.0 to 12.0, at all times until the reaction is stopped(step iii) above). Furthermore, during the neutralization reaction, itis appropriate to carry out one or both of stirring and circulation ofthe slurry. In particular, the higher the stirring speed and thecirculation speed, the more the aggregation of the hydrous silica can besuppressed, which is favorable for the production of the hydrous silicaof the present invention.

The step of stopping the neutralization reaction of step iv) is carriedout by stopping the addition of the alkali silicate aqueous solution andcontinuing the dropwise addition of only the mineral acid. It isappropriate to continue the dropwise addition of the mineral acid onlyuntil pH of the reaction solution (slurry) becomes less than 7.

Filtration and water washing of the hydrous silica in step v) may beperformed by, for example, a filter press or the like, or a filter presshaving a pressing function may be used to perform water washing and thenpress may be added.

Step vi) is a drying step in which the moisture content is controlled toa predetermined value. The method of the drying step is not particularlylimited, and specifically, a static drying method may be employed, and amethod of controlling by a commercially available dryer such as a spinflash dryer in addition to the above-mentioned spray dryer can beexemplified. If granulation is also carried out in addition to drying byany of these drying methods, compaction of step vii) can be omitted. Thegranulation can be carried out by appropriately setting the conditionsaccording to the drying method.

<Use of Additives>

After washing with water, an additive (aluminum, surfactant, silanecoupling agent, or the like) for improving the rubber reinforcingproperty may be added in advance. However, since the hydrous silica ofthe present invention is easy to obtain high reinforcing property evenif these additives are not added at all, it is preferable to add theadditives at the time of compounding the rubbers described later. Whenthe additive is inevitably added, for example, a method in which wateris added to the hydrous silica cake obtained in step v) to bere-slurried and then the additive is added and dried by a spray dryer orthe like can be exemplified.

Step vii) is a step of compacting the hydrous silica obtained in thedrying step. By compacting, the pore volume and its structure of 1.6 μmto 62 μm (1,600 to 62,000 nm) radius can be controlled. As describedabove, although it can be controlled only by the above step vi), it ispreferable to compact the dried hydrous silica from the standpoint ofstably controlling structure property. Further, compaction is preferablefrom the viewpoint that the residual amount when classified by a sievehaving an aperture of 200 μm or more can be 70% by weight or more andthe pellet hardness can be 5 to 35 cN.

As a specific compaction method, a molding machine by a commerciallyavailable dry method can be used, but there is no particularrestriction. There are roughly three types of compaction methods, i.e.,mixing molding, forced molding, and heat to utilizing molding. In thepresent invention, it is particularly preferable to use forced molding.

The forced molding method further includes a compaction method such as acompressing roll, a briquetting roll, and tableting, an extrusionmolding method using screws, and the like, and in the present invention,it is particularly preferable to use a consolidation molding method. Onthe other hand, an excessive compaction machine such as a tablet pressis not preferable because the pores structure of the hydrous silica maybe excessively crushed, so that the object of the present invention maynot be achieved.

In the case of a commercially available roll-type molding machine, apowder of hydrous silica is pressed and compressed between rotatingpress rolls while being pressurized by the rotational of a feed screw,and compact into a plate shape or a granular shape. The press rolls maybe smooth, grooved, corrugated, etc., and any roll may be used in thepresent invention. In any case, the roll shape, the speed, the pressure,and the like are adjusted so as to obtain an appropriate pore size,particle size, and pellet hardness as described above.

Methods such as granulation and compaction are commonly used in hydroussilica for rubber reinforcing filler in order to further improve thedust generation and handling performance of hydrous silica.

Although the BET specific surface area of hydrous silica of the presentinvention is 230 m²/g or more, the pore volume of 1,000 nm or less(micropores to macropores) is less likely to change even when thehydrous silica is granulated or compacted under certain conditions, sothat good rubber reinforcement can be maintained. Therefore, even if thecompaction or granulation under moderate constant conditions, it actsonly to improve handling performance and the prevention of dustgeneration, the rubber reinforcing property is not lowered.

<Rubber Compounding>

The hydrous silicate of the present invention can be used as areinforcing filler for various rubber compositions, and the use of therubber composition includes not only tires but also industrial partssuch as belts. The rubber composition which can use (include) thehydrous silicate of the present invention is not particularly limited,and may be a rubber composition including a natural rubber (NR) or adiene-based synthetic rubber alone or a blend thereof. Examples ofsynthetic rubbers include synthetic polyisoprene rubber (IR), butadienerubber (BR), styrene butadiene rubber (SBR), acrylonitrile butadienerubber (NBR), butyl rubber (IIR) and the like.

The hydrous silica of the present invention can be compounded in anamount of, for example, 5 to 100 parts by weight with respect to 100parts by weight of natural rubber and/or diene-based synthetic rubber.However, this range is not intended to be limiting.

<Additives for Rubber Compounding>

In the above rubber composition, various additives used in the rubbercomposition such as aluminum compound, silane coupling agent, surfactantand the like can be added (in addition to being added to the hydroussilica) as required at the time of rubber compounding.

When the hydrous silica of the present invention is used in rubbercompositions, in addition to the above-mentioned rubber (additive),compounding ingredients commonly used in the rubber industry such ascarbon black, softeners (waxes, oils), aging inhibitors, vulcanizingagents, vulcanizing accelerators, and the like can be appropriatelycompounded as required. The rubber composition can be prepared by acommercial mixing machine such as a mixing roll or a Banbury mixer usingthe above rubber component, hydrous silica, silane coupling agent, andthe above carbon black, rubber blending agent, or the like compounded asnecessary.

The mixing rubber composition is molded into a desired shape and thenvulcanized into various rubber products.

Rubber compositions containing the present invention hydrous silica canbe suitably applied to rubber products such as tires, conveyor belts,hoses, and the like, and rubber products such as tires, conveyor belts,hoses, and the like, which become products, are excellent in reinforcingproperties, high wear resistance, and the like. In addition, a pneumatictire using a rubber composition containing a hydrous silica of thepresent invention can be obtained by using the above rubber compositionfor a tire tread portion, and a pneumatic tire excellent in reinforcingproperty and high wear resistance of the tire tread portion can beobtained.

EXAMPLES

The present invention is further specifically described on the basis ofExamples. However, the Examples are illustrative of the presentinvention, and the present invention is not intended to be limited tothe Examples.

Determination of the Physical Properties of Hydrous Silica

BET Specific Surface Area (N₂ Specific Surface Area)

Fully Automated Specific Surface Area Measurements device (Model:Macsorb (R) HM model-1201; manufactured by Mountec Corporation) was usedfor measurement by the one-point method.

CTAB Specific Surface Area

Measurements were based on JIS K 6430 (Rubber compounding ingredientssilica test methods). However, the adsorption cross-sectional area ofCTAB molecules was calculated as 35 Å².

Pore Distribution by Nitrogen Adsorption/Desorption Method

Barret-Joyner-Halenda method (BJH method) was used to measure the totalpore volume (V_(N2)) between 1.6 nm and 100 nm, using the accurategas/vapor suction metric device (model: Belsorp max; manufactured byBell, Japan). The measurement results are the pore distribution and porevolume on the desorption side (measured from the larger pore volume).

Pore Distribution by Mercury Press-In Method 1 [Pore Radius 1.9 to 1,000nm]

Mercury porosimeter (model: PASCAL 440; manufactured by ThermoQuest) wasused to measure mercury pore distributions and pore volumes ranging from100 kPa to a maximum pressure of 400 MPa and pore radius ranging from1.9 to 6,400 nm. The measurement results are the pore distribution andpore volume measured at the time of pressure rise (from the larger porevolume). The measured results were analyzed by the attached software,and the pore volume of 1.9 to 100 nm (V_(HP-Hg)), the ratio of the porevolume of 100 to 1,000 nm to the pore volume (V_(N2)) by the nitrogenadsorption/desorption method V_(HP-Hg)/V_(N2) and so on were calculated.

Pore Distribution by Mercury Press-In Method 2 [Pore Radius 1.6 to 62 μm(1,600 to 62,000 nm)]

Mercury porosimeter (model: PASCAL 140; manufactured by ThermoQuest) wasused to measure mercury pore distributions and pore volumes ranging from10 kPa to 400 kPa and pore radius ranging from 1,600 to 62,000 nm (or1.6 to 62 μm). The pore volume (hysteresis pore volume difference) wasalso measured when the pressure was further increased to 400 kPa andthen decreased to 10 kPa. Molded hydrous silica of about 1.5 mm wasmeasured.

Measurement of pH

Based on JIS K 5101-17-2 (pigment test method), pH of slurry adjusted to4% by pure water was measured at a stable value of the indicated valueusing a commercial glass-electrode pH meter (model: F-53; manufacturedby HORIBA, LTD., Ltd.).

Electric Conductivity

4 g hydrous silica (105° C., heat loss after drying for 2 hours is 6% orless) was added to 50 ml of distilled water, mixed well, and boiled for5 minutes. The total volume was then adjusted to 100 ml using distilledwater, filtered off, and the filtrate was measured using a conductivitymeter (model: CM30R; manufactured by Toa DKK).

Moisture Content

The weight loss after drying at 105° C. for 2 hours was determined basedon JIS K 5101-15-1 (Pigment Test Procedure).

Pellet Hardness

Pellet hardness of JIS K 6219-3 (Carbon Black for RubberIndustry—Characteristics of pelletized carbon black) based on Method B,sieves were stacked in the order of an aperture of 1.4 mm and anaperture of 1.7 mm, the samples were placed on the 1.7 mm sieve, andshaken. Thereafter, 20 pelletized particles on a 1.4 mm sieve weremeasured, and an average value was obtained as the hardness of thepelletized particles.

Sieve Residue

Based on the manual sieving of JIS K 0069 dry sieving test method, thesieve was tilted 20 degrees using a 200 micron sieve, and the sieve wasmanually tapped at a rate of 120 times per minute and calculated fromthe residual weight on the sieve.

Rubber Formulation Preparation Method and Related Methods for MeasuringPhysical Properties

Formulation Preparation Method 1

A sample for rubber test was prepared according to the following mixingprocedure according to the formulation shown in Table 1. 100 parts byweight of a commercially available NBR (acrylonitrile butadiene rubber)was wrapped around an 8-inch open roll, masticating was performed for 3minutes, and then Formulation A was sequentially added over 35 minutes.After the masterbatch was cooled at room temperature, 30 parts by weightof the hydrous silica of Formulation B was mixed sufficiently again withthe 8-inch open roll to obtain an unvulcanized rubber composition.

Measurement of Dust Concentration

When the hydrous silica was mixed into the masterbatch, a digital dustmeter (type: LD-5D; manufactured by Shibata Scientific Co.) wasinstalled at 30 cm directly above the 8-inch open roll, and dust wasmeasured when 30 parts by weight of the hydrous silica was put into themasterbatch. The mass concentration conversion factor (K value, dustconcentration=K value×CPM) was calculated from the relative dustconcentration (CPM) measured by a digital dust meter, and converted tothe dust concentration (g/m³).

TABLE 1 Amount of Formulation compounding Remarks Polymer NBR 100Acrylonitrile butadiene rubber (Nipol 1042, manufactured by ZeonCorporation) Formulation A Stearic acid 1.5 (Tsubaki, manufactured byNOF Corporation) Zinc oxide 5.0 Zinc oxide (Class 2, manufactured bySakai Chemical Industry Co.) Rubber 1.5N-cyclohexyl-2-benzothiazolylsulfenamide accelerator 1 (SANCELER CZ,manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) Rubber 1.5Tetramethylthiuram disulfide accelerator 2 (NOCCELER TT-P, manufacturedby Ouchi Shinko Chemical Industrial Co., Ltd.) Sulfur 0.7 Powder sulfur200 mesh (Tsurumi Chemical Co., Ltd.) Aging inhibitor 1.5N-phenyl-N′-isopropyl-p-phenylenediamine (NOCRAC 810-NA, manufactured byOuchi Shinko Chemical Industrial Co., Ltd.) Formulation B Hydrous silica30 ※ The units in the table are phr (parts by weight based on 100 partsby weight of polymer).

Formulation Preparation Method 2

A sample for rubber test was prepared according to the following mixingprocedure according to the formulation shown in Table 2.

(i) 1.7 L Banbury mixer (manufactured by Kobe Steel) 700 g of polymerwas masticated for 30 seconds, and the Formulation A in Table 2 wasadded. The compound temperature at the time of removal was adjusted byram pressure and rotational speed so that the temperature was 140 to150° C., and it was taken out after mixing for 5 minutes.

(ii) After the compound was cooled at room temperature, Formulation B ofTable 2 was added in a 1.7 L Banbury mixer and mixed for 50 seconds (thetemperature at the time of removal was set to 100° C. or less), andsheeting was performed in an 8-inch open roll to obtain an unvulcanizedrubber composition.

TABLE 2 Amount of Formulation compounding Remarks Polymer SBR 80Styrene-butadiene rubber (SL-552, manufactured by JSR Corporation) IR 20Isoprene rubber (IR2200, manufactured by JSR Corporation) Formulation AHydrous silica 45 Stearic acid 2.0 (Tsubaki, manufactured by NOFCorporation) The silane Variable Bis(triethoxysilylpropyl) tetrasulfidecoupling agent (KBE-846, manufactured by Shin-Etsu Chemical Co., Ltd.)Formulation B Zinc oxide 3.0 Zinc oxide (Class 2, manufactured by SakaiChemical Industry Co.) Aging 1.0N-phenyl-N′-isopropyl-p-phenylenediamine inhibitor (NOCRAC 810-NA,manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) Rubber 1.21,3-diphenylguanidine accelerator 1 (SANCELER D, manufactured by OuchiShinko Chemical Industrial Co., Ltd.) Rubber 1.5N-cyclohexyl-2-benzothiazolylsulfenamide accelerator 2 (NOCCELER CZ,manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) Sulfur 1.5Powder sulfur 200 mesh (manufactured by Tsurumi Chemical Co., Ltd.) ※The units in the table are phr (parts by weight based on 100 parts byweight of polymer). ※ Amount of silane coupling agent mixed (variable) =CTAB specific surface area × 0.029 − 0.185.

Formulation Preparation Methods 1 and 2

Although the Formulation Preparation Methods 1 and 2 are not generallycomparable, the mechanical strength (share of the formulation) at thetime of compounding is weaker in the Formulation Preparation Method 1and the difference is easier to distinguish. The Formulation PreparationMethod 1 is relatively close to the formulation used in industrialrubber and the like, and the Formulation Preparation Method 2 is closeto the formulation used in the tread portion of the tire. Since thephysical properties of rubbers differ depending on the formulation, thepresent invention conducted the respective compounding tests to confirmthe change in physical properties due to the difference in the type offormulation.

Vulcanization

The unvulcanized rubber composition was placed in a test piece moldingdie and vulcanized in a steam vulcanizing press (manufactured bySuetsugu Iron Works) at a temperature of 150° C. under a pressure of 4.0to 18 MPa for 10 to 20 minutes to obtain test pieces.

The test piece mold used for vulcanization was as follows.

-   -   Tear strength measuring die (model: MP-124NJKAC; manufactured by        Dumbell)    -   Dispersibility measuring die (model: MPA-609AK; manufactured by        Dumbell)    -   Abrasion test die (model: MPL-309LAKC; manufactured by Dumbell)

Dispersibility Evaluation

Based on ISO 11345, the test piece cross section after vulcanization wasmeasured using Dispergrader 1000 (manufactured by OPTIGRADE Co.). Thedegree of dispersion was evaluated as the X value. The larger the value,the better the dispersibility, and the evaluation was performed in fourstages of A, B, C, and D. In Formulation Preparation Method 1, X valuesof >8.5 were defined as A, 8.0 to 8.5 as B, 7.5 to 8.0 as C, and lessthan 7.5 as D. In Formulation Preparation Method 2, X values of >8.0were defined as A, 7.5 to 8.0 as B, 7.0 to 7.5 as C, and less than 7.0as D. In both cases, B or higher was considered acceptable.

Tear Strength

JIS K 6252-1 (vulcanized rubber and thermoplastic rubber-how todetermine the tear strength-) based on the test method B, the vulcanizedrubber sheet, punched into an angle type (without notches) using acutting machine, the shopper-type tensile testing machine (manufacturedby Shimadzu Corporation) tensile until the test piece was broken, it wasdetermined the tear strength. Measurement results were obtained by theindex in the case of reference example 1 being 100 (reference). Thehigher the index, the higher the tear strength, which was evaluated in 4stages of A, B, C, and D. In Formulation Preparation Method 1, when thetear strength was improved by 15% or more from the standard (index 115or more), the tear strength was A, when the tear strength was improvedby 5 to 10% (index 105 to 110) was B, when the tear strength wasequivalent to the standard (index 95 to 105) was C, and when the tearstrength was worsened from the standard (index less than 95) was D. InFormulation Preparation Method 2, tear strength increased by 10% or morefrom the standard (index 110 or more) was defined as A, that increasedby 5 to 10% (index 105 to 110) was defined as B, that comparable to thestandard (index 95 to 105) was defined as C, and that worsened from thestandard (index 95 or less) was defined as D. In both cases, B or higherwas considered acceptable.

Wear Resistance Test

Based on JIS K 6264-2 (vulcanized rubber and thermoplastic rubber-how todetermine the wear resistance-), the results were measured with anAkron-type wear tester. A test piece of diameter φ63.5 mm, a thicknessof 12.7 mm and the center hole 12.7 mm was set, after running-inoperation 1,000 revolutions at the inclination angle 15°, load 27N, anda rotation speed of 75 rpm of the test piece, the test 1,000 revolutionsin the same conditions was conducted and then wear volume reduction wasmeasured. Measurement results were obtained by the index in the case ofreference example 1 being 100 (reference). The higher the index, thebetter the wear resistance, and the evaluation was carried out in fourstages of A, B, C, and D. In Formulation Preparation Method 1, when thewear resistance was improved by 20% or more from the standard (index 120or more), it was A, when the wear resistance was improved by 10 to 20%(index 110 to 120), it was B, when the wear resistance was equivalent tothe standard (index 90 to 110), it was C and when the wear resistancewas worsened from the standard (index 90 or less), it was D. InFormulation Preparation Method 2, the case where the wear resistance wasimproved by 30% or more from the standard (index 130 or more) wasdesignated as A, the case where the wear resistance was improved by 10to 30% (index 110 to 130) was designated as B, the case where the wearresistance was equivalent to the standard (index 90 to 110) wasdesignated as C, and the case where the wear resistance was worsenedfrom the standard (index 90 or less) was designated as D. In both cases,B or higher was considered acceptable.

Example 1

Hydrous silica was produced and evaluated through the following steps i)to vii). Steps i) to iv) below were carried out in a 240-liter stainlesssteel container equipped with a stirrer and a circulation pump whilemaintaining the temperature at 76° C. while constantly stirring andcirculating. As the aqueous solution of sodium silicate described below,No. 3 sodium silicate having a SiO₂ concentration of 12.8 wt %, a Na₂Oconcentration of 4.0 wt %, and a SiO₂/Na₂O molar ratio of 3.2 was used,and 95 wt % concentrated sulfuric acid was used as sulfuric acid.

i) An aqueous solution of sodium silicate was added to 80 liters of warmwater until pH reached 11.5.

ii-1) 1.06 liters of sulfuric acid was added dropwise simultaneously for35 minutes with aqueous sodium silicate solution whose flow rate wasadjusted to maintain pH 11.5.

ii-2) The addition of aqueous sodium silicate solution was then stoppedand only sulfuric acid was added dropwise until pH reached 11.0.

ii-3) The aqueous solution of sodium silicate and sulfuric acid weresimultaneously added dropwise for 15 minutes at the same flow rate as instep ii-1) while maintaining pH at 11.0.

iii) The flow rates of the aqueous solution of sodium silicate andsulfuric acid were adjusted so that the flow rates of the aqueoussolution of sodium silicate and sulfuric acid were 43% with respect tothe steps ii-1) and ii-3), and were simultaneously added dropwise over60 minutes while maintaining pH 11.0.

iv) The dropping of the aqueous solution of sodium silicate was stopped,and only sulfuric acid was dropped to lower the pH, and when pH reached3.0, the dropping of sulfuric acid was also stopped to completelyterminate the neutralization reaction, and a hydrous silica slurry wasobtained.

v) The obtained hydrous silica slurry was filtered by a filter press andwashed with water to obtain a hydrous silica cake.

vi) The hydrous silica cake was slurried by adding water so as to have aSiO₂ content of 120 g/liter, and then dried using a spray dryer (type:AN-40R type: made by Ashizawa Niloatomizer) so that the moisture contentwas less than 9%.

vii) The obtained dry powder was mixed and compacted using a rollercompacting machine (Roller compactor, model: FR125×40 model manufacturedby Turbo Industry Co., Ltd.) and an attached screw feeder to obtain ahydrous silicic acid compacting. Note that the conditions for mixing andcompacting were a feed rate of 11.3 kg/h, a roll interval of 1.05 mm, acompression pressure of 0.3 ton/cm, and a roll speed of 8 rpm.

Example 2

Hydrous silica was produced and evaluated through the following steps i)to vii). The device, the aqueous solution of sodium silicate, thesulfuric acid, and the temperatures up to the step i) were carried outunder the same conditions as in the EXAMPLE 1.

i) An aqueous solution of sodium silicate was added to 80 liters of warmwater until pH reached 11.5.

ii-1) Sulfuric acid alone was then added dropwise to lower the pH to11.0.

ii-2) 0.76 liters of sulfuric acid were added dropwise simultaneouslyfor 25 minutes with aqueous sodium silicate solution whose flow rate wasadjusted to maintain pH 11.0.

iii-1) For step ii-2), the flow rate was adjusted so that the flow rateof the aqueous solution of sodium silicate and the flow rate of sulfuricacid became 43%, and simultaneously dropped over 25 minutes whilemaintaining pH 11.0.

ii-3) The aqueous solution of sodium silicate and sulfuric acid weresimultaneously added dropwise for 20 minutes at the same flow rate as instep ii-2) while maintaining pH at 11.0.

iii-2) Next, while maintaining pH at 11.0, the aqueous solution ofsodium silicate and sulfuric acid were simultaneously added dropwise for40 minutes at the same flow rate as in the step iii-1).

Thereafter, steps iv) to vi) were carried out under the same conditionsas in Example 1.

vii) Except for that the feed amount of the dry powder obtained in vi)was increased to 11.5 kg/h, a compacted hydrous silica was obtained bycompacting under the same conditions as in Example 1.

Example 3

Hydrous silica was produced and evaluated through the following steps i)to vii). The device, the aqueous solution of sodium silicate, thesulfuric acid, and steps up to step i) were carried out under the sameconditions as in Example 1, except that the temperatures were set to at81° C.

i) An aqueous solution of sodium silicate was added to 80 liters of warmwater until pH reached 11.5.

ii-1) 0.61 liters of sulfuric acid were added dropwise simultaneouslyfor 20 minutes with aqueous sodium silicate solution whose flow rate wasadjusted to maintain pH 11.5.

ii-2) The addition of aqueous sodium silicate solution was then stoppedand only sulfuric acid was added dropwise until pH reached 11.0.

ii-3) The aqueous solution of sodium silicate and sulfuric acid weresimultaneously added dropwise for 30 minutes at the same flow rate as instep ii-1) while maintaining pH at 11.0.

iii) The flow rates of the aqueous solution of sodium silicate andsulfuric acid were adjusted so that the flow rates of the aqueoussolution of sodium silicate and sulfuric acid were 43% with respect tothe steps ii-1) and ii-3), and were simultaneously added dropwise over60 minutes while maintaining pH 11.0.

Thereafter, steps iv) to vi) were carried out under the same conditionsas in Example 1.

vii) Except for that the feed amount of the dry powder obtained in vi)was increased to 13.2 kg/h, a compacted hydrous silica was obtained bycompacting under the same conditions as in Example 1.

Example 4

Hydrous silica was produced and evaluated through the following steps i)to vii). The device, the aqueous solution of sodium silicate, and thesulfuric acid were carried out under the same conditions as in Example1, except for that the temperatures were set to at 85° C.

i) An aqueous solution of sodium silicate was added to 80 liters of warmwater until pH reached 11.7.

ii-1) Sulfuric acid alone was then added dropwise to lower the pH to11.0.

ii-2) 1.52 liters of sulfuric acid were added dropwise simultaneouslyfor 50 minutes with aqueous sodium silicate solution whose flow rate wasadjusted to maintain pH 11.0.

iii) The flow rate was adjusted so that the flow rate of the aqueoussolution of sodium silicate and the flow rate of sulfuric acid became43% with respect to the process ii-2), and simultaneously dropped over60 minutes while maintaining pH 11.0.

Thereafter, steps iv) to vi) were carried out under the same conditionsas in Example 1.

vii) Except for that the feed amount of the dry powder obtained in vi)was increased to 11.6 kg/h, a compacted hydrous silica was obtained bycompacting under the same conditions as in Example 1.

Example 5

Hydrous silica was produced and evaluated through the following steps i)to vii). Except for that the temperatures were set to at 87° C., thedevice, the aqueous solution of sodium silicate, and the sulfuric acidwere carried out under the same conditions as in Example 1.

i) An aqueous solution of sodium silicate was added to 80 liters of warmwater until pH reached 11.6.

ii-1) 1.06 liters of sulfuric acid was added dropwise simultaneously for35 minutes with aqueous sodium silicate solution whose flow rate wasadjusted to maintain pH 11.5.

ii-2) The addition of aqueous sodium silicate solution was then stoppedand only sulfuric acid was added dropwise until pH reached 11.0.

ii-3) The aqueous solution of sodium silicate and sulfuric acid weresimultaneously added dropwise for 15 minutes at the same flow rate as instep ii-1) while maintaining pH at 11.0.

iii) The flow rates of the aqueous solution of sodium silicate andsulfuric acid were adjusted so that the flow rates of the aqueoussolution of sodium silicate and sulfuric acid were 43% with respect tothe steps ii-1) and ii-3), and were simultaneously added dropwise over60 minutes while maintaining pH 11.0.

Thereafter, steps iv) to vi) were carried out under the same conditionsas in Example 1.

vii) Except for that the feed amount of the dry powder obtained in vi)was increased to 11.7 kg/h, a compacted hydrous silica was obtained bycompacting under the same conditions as in Example 1.

Reference Example 1

Nipsil KQ (made by Tosoh-Silica) was used as an example of hydroussilica, which has a BET-specific surface area of 220 m²/g or more and iscommercially available as hydrous silica for rubber-reinforcing fillers.The physical properties of the rubber compound, such as the wearresistance and the tear strength, were evaluated by an index using thephysical properties of Nipsil KQ as a reference (100).

Comparative Example 1

Silica cake was produced in the same formulation as the method describedin Example 5 of JP-A-2017-514773 (Patent document 1), to obtain ahydrous silica in the form of substantially spherical beads having a BETspecific surface area of 250 m²/g.

The same device (reactor) as in Example 1 was used for the production,and neutralization of hydrous silica was synthesized at a dosage of 1/11of that of Example 5 in JP-A-2017-514773, and after the silica cake wasobtained by filtration with a filter press, the solution was dried sothat the moisture content was less than 9% by the process of step vi) ofExample 1, except for that a predetermined amount of a sodium aluminatesolution and a neutralization solution were added. However, theoperation of the step vii) of Example 1 was not performed according tothe method of the prior art document 1.

Comparative Example 2

Using the same reaction vessel as in Example 1 in the same formulationas in Example 1 of JP-A-H10-194722, to obtain a hydrous silica by themethod of box-type drying. The production was carried out at a dose of1.2 times that of Example 1 of JP-A-H10-194722.

Comparative Example 3

Using the same reaction vessel as in Example 1, a hydrous silica wasproduced in the same formulation as in Example 2 of JP-A-2012-17440,followed by compacting the hydrous silica under the same conditions asin step vii) of Example 4 to obtain a compacted hydrous silica. Theproduction was carried out at a 1.3-fold dose compared to ProductionExample 2 of JP-A-2012-17440.

In the manufacturing methods of Comparative Examples 1 to 3, there is nostep corresponding to step iii) of Examples 1 to 5. Further, in themanufacturing methods of Comparative Examples 1 and 2, there is no stepcorresponding to the step vii) of Examples 1 to 5.

Description of Results <Pore>

FIG. 1 shows a comparison of the cumulative pore volume of the hydroussilica obtained in Example 1 with a pore radius of less than 100 nmmeasured by the nitrogen adsorption/desorption method and the mercurypress-in method.

From comparison results, it can be seen that the pores of the hydroussilica of Example 1 having a size of less than 100 nm have a smallerpore volume (V_(HP-Hg)<V_(N2)) when measured by the mercury press-inmethod (V_(HP-Hg)) than when measured by the nitrogenadsorption/desorption method (V_(N2)).

FIGS. 2 to 4 show pore distribution diagrams including cumulative porevolumes of the nitrogen adsorption/desorption method (measurement ranger=1.6 to 100 nm), mercury press-in method 1 (measurement range r=1.9 to6,400 nm), and the mercury press-in method 2 (measurement range r=1.6 to62 μm [1,600 to 62,000 nm]) obtained in Example 1.

From these figures and measured data, the pore volume (V_(N2)) by thenitrogen adsorption/desorption method, the pore volume (V_(HP-Hg)) inthe range of 1.9 to 100 nm and the pore volume in the range of 100 to1,000 nm by the mercury press-in method, the pore volume in the range of1.6 to 62 pm (1,600 to 62,000 nm) by the mercury press-in method and thehysteretic pore volume difference, i.e., the pore volume when pressurewas raised and then depressurized, were obtained.

Results Description (Table)

The physical properties of the hydrous silica of Examples 1 to 5 andComparative Examples 1 to 3 are shown in Table 3, and the results of therubber compounding test are shown in Table 4.

TABLE 3-1 Hydrous silica properties of the examples EXAMPLES Preferably1 2 3 4 5 Physical Moisture content % Less than 9% 4.0 3.5 4.1 3.6 4.3properties pH(4% Susp.) 5-8 6.0 5.6 6.2 6.0 6.4 of hydrous Electricconductivity μS/cm 1,000 Less than 45 82 64 45 40 silica BET specificsurface area m²/g 230-350 322 293 277 256 241 Mercury pore volume cm³/g1.40-2.00 1.64 1.74 1.71 1.82 1.69 High pressure side Vol. [V_(HP-Hg)]r: 1.9-100 nm Nitrogen desorption side cm³/g 1.60-2.20 2.06 1.92 2.042.06 2.01 Vol. [V_(N2)] r: 1.6-100 nm V_(HP-Hg)/V_(N2) ratios —0.70-0.95 0.80 0.91 0.84 0.88 0.84 Mercury pore volume cm³/g 0.50-1.000.51 0.66 0.62 0.74 0.87 Medium pressure side Vol. r: 100-1,000 nmMercury pore volume cm³/g 0.18-0.80 0.31 0.26 0.18 0.43 0.24 Lowpressure side Hysteresis 0.07 or more 0.11 0.11 0.10 0.18 0.12 Vol. r:1.6-62 μm cm³/g (1,600-62,000 nm) CTAB specific surface area m²/g200-350 273 247 238 243 205 Pellet hardness cN  5-35 11 19 32 18 20Residue on sieve %   70 or more 80 85 90 90 85

TABLE 3-2 Physical properties of hydrous silica in Reference Examplesand Comparative Examples Reference Comparative Example Preferablyexample 1 1 2 3 Physical Moisture content % Less than 9% 6.0 4.6 4.7 5.8properties pH 5-8 6.1 6.6 6.2 5.9 of hydrous Electric conductivity μS/cm1,000 Less than 146 408 72 217 silica BET specific surface area m²/g230-350 222 250 255 262 Mercury pore volume cm³/g 1.40-2.00 1.65 1.591.50 1.44 High pressure side Vol. [V_(HP-Hg)] r: 1.9-100 nm Nitrogendesorption side cm³/g 1.60-2.20 1.60 1.61 1.51 1.42 Vol. [V_(N2)] r:1.6-100 nm V_(HP-Hg)/V_(N2) ratios — 0.70-0.95 1.03 0.99 0.99 1.01Mercury pore volume cm³/g 0.50-1.00 0.55 0.34 0.72 0.41 Medium pressureside Vol. r: 100-1,000 nm Mercury pore volume cm³/g 0.18-0.80 1.63 1.531.92 1.06 Low pressure side Hysteresis 0.07 or more 0.40 0.44 0.63 0.31Vol. r: 1.6-62 μm cm³/g (1,600-62,000 nm) CTAB specific surface aream²/g 200-350 205 250 139 191 Pellet hardness cN  5-35 CNM CNM CNM 24Residue on sieve %   70 or more 0 0 0 95 CNM: Could not be measured

TABLE 4 Results of Rubber Compound Test by Formulation PreparationMethod 1 (FP Method 1) and Formulation Preparation Method 2 (FP Method2) EXAMPLES 1 2 3 4 5 FP Method 1 Dust Concentration A: less than 1.51.0 A 1.3 A 1.6 B 1.2 A 1.5 B mg/m³ B: 1.5-3.0 C: 3.0-4.5 D: 4.5 or moreDispersibility Evaluation A: 8.5 or more 8.7 A 8.3 B 8.4 B 8.5 A 8.7 AX-value B: 8.0-8.5 C: 7.5-8.0 D: less than 7.5 Tearing Strength Index A:115 or more 121 A 121 A 119 A 116 A 112 B B: 105-115 C: 95-105 D: lessthan 95 Wear resistance Index A: 120 or more 129 A 124 A 114 B 119 B 116B B: 110-120 C: 90-110 D: less than 90 FP Method 2 DispersibilityEvaluation A: 8.0 or more 8.3 A 8.0 A 7.9 B 8.1 A 8.3 A X-value B:7.5-8.0 C: 7.0-7.5 D: less than 7.0 Tearing Strength Index A: 110 ormore 110 A 109 B 109 B 113 A 106 B B: 105-110 C: 95-105 D: less than 95Wear resistance Index A: 130 or more 169 A 145 A 135 A 128 B 119 B B:110-130 C: 90-110 D: less than 90 Reference Comparative Example example1 1 2 3 FP Method 1 Dust Concentration A: less than 1.5 1.2 A 4.4 C 4.5D 0.8 A mg/m³ B1.5-3.0 C: 3.0-4.5 D: 4.5 or more DispersibilityEvaluation A: 8.5 or more 7.7 C 6.7 D 8.8 A 7.8 C X-value B: 8.0-8.5 C:7.5-8.0 D: less than 7.5 Tearing Strength Index A: 115 or more 100 C 107B 95 C 93 D B: 105-115 C: 95-105 D: less than 95 Wear resistance IndexA: 120 or more 100 C 45 D 64 D 65 D B: 110-120 C: 90-110 D: less than 90FP Method 2 Dispersibility Evaluation A: 8.0 or more 7.4 C 7.4 C 8.7 A7.4 C X-value B: 7.5-8.0 C: 7.0-7.5 D: less than 7.0 Tearing StrengthIndex A: 110 or more 100 C 98 C 103 C 94 D B: 105-110 C: 95-105 D: lessthan 95 Wear resistance Index A: 130 or more 100 C 77 D 87 D 76 D B:110-130 C: 90-110 D: less than 90

Discussion (Description)

In the Examples of Table 3-1, the hydrous silica is all(V_(HP-Hg)<V_(N2)) and V_(HP-Hg)/V_(N2) ranges from 0.70 to 0.95.

In the evaluation of the wear resistance and the tear strength in Table4, both of the compound preparation methods 1 and 2 show a remarkableimprovement effect as compared with the comparative example.

Particularly, the improvement effect of the wear resistance isremarkable, and at the same time, in addition to the improvement of thereinforcing property, the powder standing is less and the handlingperformance is also kept.

Reference example 1 is a commercially available hydrous silica having alow dust concentration and good workability, although the pellethardness was not measurable because of the granular state of fineparticles. (Evaluation Standard for Rubber Physical Properties)

Comparative Example 1 is a hydrous silica with the BET specific surfacearea is greater than or equal to 230 m²/g but withV_(HP-Hg)/V_(N2)=0.99. Although there is a possibility that the dustconcentration and the like can be improved by performing the compaction,the dispersibility in the rubber and the reinforcing property wereexpected to be further lowered, and therefore, the rubber physicalproperties were evaluated without performing the compaction.

Comparative Example 2 exhibits high V_(HP-Hg)/V_(N2)=0.99. Further,since CTAB specific surface area is also low, high reinforcement,particularly high wear resistance, has not been obtained. In addition,although dust density may be improved by densely-forming, it is unlikelythat rubber reinforcement (particularly the wear resistance) can beimproved remarkably because of V_(HP-Hg)/V_(N2)=0.99.

Comparative Example 3 is a hydrous silica having a BET specific surfacearea of 230 m²/g or more with a low dust concentration during mixing andexcellent handling performance by compacting. However, sinceV_(HP-Hg)/V_(N2)=1.01, dispersion in the rubber is not enough andreinforcement is also insufficient.

In summary, since the hydrous silica of Examples 1 to 5 has a highspecific surface area and a V_(HP-Hg)/V_(N2) of 0.70 to 0.95, high wearresistance and high tear strength are obtained when mixed into rubbers.In addition, it has a feature that it is easy to disperse even when itis compacted, and it is understood that it is an excellent hydroussilica having improved workability. In particular, Example 1 exhibitsV_(HP-Hg)/V_(N2)=0.80, a low value, the effects of the wear resistanceimprovement is significant.

As explained above, the hydrous silica of the present invention has aBET specific surface area ranging from 230 to 350 m²/g, but pores with apore radius of 100 nm or less tend to collapse as compared withconventional hydrous silica, and pores with a pore radius of 100 to1,000 nm and 1.6 μm or more also have moderate structure. Therefore, itcan be compounded into rubber with improved handling performance, andwhen compounded, it can be dispersed well, and high reinforcingproperties (particularly the wear resistance) can be obtained.

Accordingly, it is possible to provide a hydrous silica having excellentrubber reinforcing properties, particularly the wear resistance, inwhich the rubber reinforcing properties are added by improving handlingperformance when compounded into the rubber, making the BET specificsurface area within a predetermined range, and improving dispersibilityof the hydrous silica into the rubber.

INDUSTRIAL APPLICABILITY

The present invention has utility in the art where hydrous silica isinvolved.

The invention claimed is:
 1. A hydrous silica for rubber reinforcingfiller having: a BET-specific surface area ranging from 230 m²/g to 350m²/g; and a) a pore volume of 1.9 nm to 100 nm pore radius measured bythe mercury press-in method (V_(HP-Hg)) ranging from 1.40 cm³/g to 2.00cm³/g; b) a total pore volume in a range of 1.6 nm to 100 nm pore radiusmeasured by the nitrogen adsorption/desorption method (V_(N2)) rangingfrom 1.60 cm³/g to 2.20 cm³/g; and c) a pore volume ratio of (a) and (b)V_(HP-Hg)/V_(N2) ranges from 0.70 to 0.95.
 2. The hydrous silicaaccording to claim 1, further comprising that a pore volume in a rangeof 100 nm to 1,000 nm of pore radius as measured by the mercury press-inmethod ranges from 0.50 cm³/g to 1.00 cm³/g.
 3. The hydrous silicaaccording to claim 1, further comprising that a pore volume in a rangeof 1.6 μm to 62 μm of pore radius measured by the mercury press-inmethod ranges from 0.18 cm³/g to 0.80 cm³/g, and a hysteretic porevolume difference in a range of 10 kPa to 400 kPa measured by themercury press-in method is 0.07 cm³/g or more.
 4. The hydrous silicaaccording to claim 1, further comprising that a CATB specific surfacearea ranges from 200 m²/g to 350 m²/g.
 5. The hydrous silica accordingto claim 1, further comprising that a pH of a 4% by weight slurry is ina range of 5 to 8, an electric conductivity of the filtrate of theslurry is less than 1,000 μS/cm, and a moisture content is less than 9%.6. The hydrous silica according to claim 2, further comprising that apore volume in a range of 1.6 μm to 62 μm of pore radius measured by themercury press-in method ranges from 0.18 cm³/g to 0.80 cm³/g, and ahysteretic pore volume difference in a range of 10 kPa to 400 kPameasured by the mercury press-in method is 0.07 cm³/g or more.
 7. Thehydrous silica according to claim 2, further comprising that a CATBspecific surface area ranges from 200 m²/g to 350 m²/g.
 8. The hydroussilica according to claim 3, further comprising that a CATB specificsurface area ranges from 200 m²/g to 350 m²/g.
 9. The hydrous silicaaccording to claim 2, further comprising that a pH of a 4% by weightslurry is in a range of 5 to 8, an electric conductivity of the filtrateof the slurry is less than 1,000 μS/cm, and a moisture content is lessthan 9%.
 10. The hydrous silica according to claim 3, further comprisingthat a pH of a 4% by weight slurry is in a range of 5 to 8, an electricconductivity of the filtrate of the slurry is less than 1,000 μS/cm, anda moisture content is less than 9%.
 11. The hydrous silica according toclaim 4, further comprising that a pH of a 4% by weight slurry is in arange of 5 to 8, an electric conductivity of the filtrate of the slurryis less than 1,000 μS/cm, and a moisture content is less than 9%.